Not applicable.
1. Field of Invention
This invention is an improved and more versatile apparatus for cutting roofing shingles.
2. Description of Prior Art
Installation of roofing shingles requires many cuts to be made in various directions. Traditional practice calls for use of a hand-held utility-type knife which is slow and inaccurate and potentially dangerous since some types of shingles need multiple passes and considerable force with the knife, which can and does slip, causing injury. Several designs have been proposed for an apparatus to cut shingles, however, these designs are limited in performance in various ways. The underlying problem is that shingles resist being cut, and particularly, cut neatly. This is due to their thickness and toughness and the wide range of workability resulting from the extremes of ambient temperature during which they are installed. In cold weather, shingles are stiff and brittle, resistant to cutting, and tend to crack without careful handling. In hot weather, they become exceedingly soft and pliable and prone to tearing. Also, in hot weather, the asphaltic component of the shingles softens into a semi-melted state and accumulates as a tarry deposit on tools. Under any weather conditions, debris and granules from the surface of the shingles are dislodged in handling and collect within the workings of an apparatus not designed to tolerate them.
A shingle cutting apparatus must also take into account that regardless of the design employed a vigorous thrust of the mechanism will be required to effect its operation, again due to the resistance of the shingle being cut. This requirement can be satisfied by proper provision for the use of leverage, however, the apparatus must be configured to remain stable in the face of the forceful stroke by the user. If the apparatus moves or tips in use, it will be inconvenient or dangerous to use.
Prior art fails to overcome these difficulties and therefore has not met with practical success. U.S. Pat. No. 5,052,256 to Morrissey and U.S. Pat. No. 4,951,540 to Cross et al disclose designs that perform only one specialized cut on only one type of shingle. Considered analysis indicates that in addition to this limitation these two designs do not allow the user to develop sufficient leverage to operate successfully under the wide range of field conditions previously mentioned.
A different apparatus is disclosed in U.S. Pat. No. 5,787,781 to Hile. In the initial stages of my own experimentation, I developed, constructed, and tested a model essentially similar to this and determined that it has several shortcomings. The blade does not consistently maintain tight contact with the edge of the work surface because of lack of sufficient rigidity both of the blade and of the pivot arrangement. A very small amount of distortion in the area of the pivot allows the blade to separate from the edge of the work surface and merely sandwich the shingle between the two instead of cutting it. This phenomenon is exacerbated by the accretion of tarry deposits on the mating surfaces of the blade and the edge of the work surface as well as the accumulation of shingle debris and detached surface granules in these deposits and in the pivot area.
Use of a precision bearing as proposed by Hile has a drawback in that it will be vulnerable to damage in the real-world conditions that prevail while roofing is being done. This type of work is frequently carried out under wet conditions; also, the tendency of shingles to generate debris particles and shed granules as previously mentioned will degrade a precision mechanism. Moreover, the need for a complex bearing in this application is questionable, since the motion anticipated is comparatively slow and sporadic and covers something less than a ninety degree arc, whereas a ball or roller bearing would be more appropriately specified in an application having greater or continuous motion and/or higher speed.
Hile shows no method of sharpening the stationary cutting edge. As the edge becomes worn, the tendency of the shingle to be sandwiched between the cutting edge and the blade will increase.
Another shortcoming of Hile derives from the position of the guide member relative to the shingle. Since the shingle resists being cut, the motion of the blade tends to force the shingle to slide away from the pivot, and therefore, away from the guide member at the beginning of the cutting stroke. This reduces the accuracy of the cut. The Hile apparatus also lacks the ability to make an accurate and repeatable angle cut. Further, there is no provision at all to produce the lengthwise cuts that are necessary for the lowest, or starting course of shingles.
Hile proposes the blade to be outside of the footprint outlined by the supporting legs. This may allow the apparatus to tip to the right in response to vigorous force on the handle. In addition, the fact that the handle extends substantially beyond the ends of the legs would tend to cause the opposite, or pivot, end of the apparatus to lift in response to the cutting stroke. Further, the apparent width between the legs of the apparatus would seem to preclude its use on the narrow scaffolding typically used on a roof.
In accordance with the present invention, a shingle cutting apparatus comprises a raised work surface with a horizontal fixed blade attached along one side, a moveable and adjustable blade assembly, and a guide fence assembly capable of being fixed at any desired location on the work surface to align a shingle for a cut.
Accordingly, several objects and advantages of my invention are as follows:
1. The triangular design of the moveable blade assembly, the use of a long pivot shaft attached on both ends, and the design of the frame all provide superior rigidity and keep the moveable and fixed blades in tight contact with each other resulting in clean shearing action. Adjustment is provided to maintain this relationship and to compensate for wear and sharpening.
2. The moveable blade is prevented from distorting by the combination of the blade brace and the triangular web between them that together form a rigid blade assembly.
3. The use of a vertical moveable blade and a horizontal, protruding fixed blade minimizes tarry buildup since the fixed blade acts as a scraper to keep the moveable blade substantially clean. Since this buildup occurs mainly on wide surfaces, the edge of the fixed blade also remains substantially clean.
4. The use of a fixed blade that protrudes beyond the side of the work surface provides clearance for the shingle cutoff, or waste piece, to curl downward during the cut and fall away without dragging on the side of the work surface, which would force the shingle out of position during the cutting stroke.
5. The use of a moveable guide fence permits accurate and repeatable angled or ninety degree cuts. A detent arrangement provides a positive stop for ninety degree cuts.
6. With the guide fence supporting the edge of the shingle furthest from the pivot shaft, the shingle is prevented from sliding in response to the action of the blade. In my apparatus the action of the blade tends to hold the shingle more securely against the guide fence.
7. The guide fence is easily repositioned on the work surface to permit length-wise cutting of shingles. A detent arrangement positively locates the guide fence parallel to the blades and automatically produces proper width cut pieces in accordance with the several standard dimensions used by shingle manufacturers.
8. The design of the pivot shaft minimizes the accumulation of shingle debris land granules that would inhibit proper operation of the moveable blade. The open end of the blade tube extends under the protruding fixed blade to deflect falling debris. More importantly, there is no precision ball or roller bearing mechanism that would be vulnerable to infiltration of debris as well as inflitration of moisture which would create rust. By eliminating a precision bearing, a potential maintainance problem due to rust or contamination is avoided and the apparatus will be simplified.
9. The design of the rear leg enables the user to anchor the device with his or her foot while operating the apparatus if desired. At the same time, the user""s foot is protected from injury since it is shielded by the raised frame.
10. The overall shape of the frame assembly is conducive to use on a scaffolding as well as on the roof surface. A leg arrangement providing three points of support results in stability of the apparatus while in use.
11. The handle of the moveable blade does not extend significantly rearward of the footprint outlined by the three points of support of the base assembly. This avoids destabilizing of the apparatus when making a cut. The fact that the blades are laterally within this footprint keeps the apparatus from tipping to the right during operation.